The present invention relates to a conjugate fiber of good workability, resistance to core/sheath peeling and deep colorability to give dyed articles.
In general, polyolefin resins such as polypropylene and polyethylene are relatively inexpensive and have good mechanical properties, and they are widely used in the field of fibers as well.
In view of their dyeability and heat resistance, however, their applications are limited and, for example, they are used mainly for non-clothing. For improving the dyeability of polyolefin fibers, known is a method of kneading pigment in them, but it is problematic in that the productivity is low and the quality of the resulting fibers is worsened to a great extent.
On the other hand, polyester resins such as polyethylene terephthalate and polybutylene terephthalate have good dyeability and heat resistance, and polyamides have good physical properties, and they are widely used in the field of fibers as well. However, they are problematic in that their specific gravity is large.
In addition, since polyolefin fibers and polyester fibers are hydrophobic, they have another drawback in that their water absorbability and moisture absorbability are not good. To overcome these drawbacks, various investigations have heretofore been made. For example, one method tried for that purpose comprises conjugate-spinning of a hydrophobic polymer such as polyester and a polymer having a hydroxyl group to thereby make the hydrophobic fibers have additional properties of hydrophilicity, etc.
Concretely, conjugate fibers of a hydrophobic thermoplastic resin such as polyester, polypropylene, polyamide or the like, and an ethylene-vinyl alcohol copolymer are disclosed in JP-B 56-5846, 55-1372, etc.
In the above-mentioned conjugate fibers, however, the adhesion of the conjugated two polymers is low at their interface and therefore the two components readily peel from each other, and this is a trouble in some use. In particular, when the fibers are worked, for example, for hard twisting or false twisting under tension applied thereto perpendicularly to the machine direction of the fibers, the conjugated components of the fibers may often peel from each other somewhere in the thus-worked fibers. If the hard-twisted or false-twisted yarns are formed into fabric and the resulting fabric is colored, the peeled part of the fibers is seen whitish and it loses the commercial value of the fabric.
An object of the invention is to provide a conjugate fiber of at least two thermoplastic resin components, which has improved workability, resistance to core/sheath peeling and deep colorability to give colored articles, not detracting from the characteristics intrinsic to these resins.
Another object is to provide a conjugate fiber which has good colorability into more vivid colors and is glossy, and further has good moisture absorbability, still keeping the above-mentioned good workability and resistance to peeling between the conjugated components.
Specifically, the invention is a core/sheath conjugate fiber which comprises a core component A of a thermoplastic polymer and a sheath component B of another thermoplastic polymer and which is characterized in that, in its cross section, the core component A has at least 10 projections or exists as an aligned group of at least 10 flattened cross-section core components, the distance (I) between the neighboring projections or between the neighboring flattened cross-section core components is at most 1.5 xcexcm, the projections or the flattened cross-section core components are so positioned that their major axes are all at an angle (Rxc2x0) of 90xc2x0xc2x115xc2x0 to the outer periphery of the fiber cross section, and the ratio (X) of the outer peripheral length (L2) of the core component A to the outer peripheral length (L1) of the conjugate fiber satisfies the following formula (1):
X/Cxe2x89xa72xe2x80x83xe2x80x83(1)
wherein X indicates the ratio of the outer peripheral length of the core component A to the outer peripheral length of the conjugate fiber (L2/L1); and C indicates the conjugate ratio by mass of the core component A to the overall conjugate fiber defined as 1.